Transmitter apparatus, receiver apparatus , transmitting method, receiving method, and program

ABSTRACT

A serial-parallel converter  102  of a transmitter apparatus receives an input of a signal to be transmitted and serial-parallel-converts this to output m (m≧2) number of intermediate signals. A unitary matrix modulator  103  modulates the output m number of intermediate signals into a unitary matrix of m rows and m columns whose components other than diagonal components are 0 and outputs the obtained matrix. A splitter  111  supplies the respective diagonal components of the output matrix to the input channels of an inverse Fourier transform unit  112  as input signals. The inverse Fourier transform unit  112  outputs m number of inverse-Fourier-transformed signals obtained by performing inverse Fourier transform of the supplied input signals. A parallel-serial converter  113  parallel-serial-converts the output m number of inverse-Fourier-transformed signals to output one transmission signal. A transmission unit  114  transmits the output transmission signal. The difference between the frequency of any two channels of the inverse Fourier transform unit  112  is equal to or larger than a predetermined coherent bandwidth.

TECHNICAL FIELD

The present invention relates to a transmitter apparatus, a receiverapparatus, a transmitting method, and a receiving method for performingefficient communication by sing modulation/demodulation by a unitarymatrix in which components other than the diagonal components are 0, anda program for realizing these on a computer.

BACKGROUND ART

Earlier techniques relating to OFDM (Orthogonal Frequency DivisionMultiplex) modulation/demodulation and earlier techniques relating tomodulation/demodulation using a unitary matrix are disclosed in theliteratures indicated below.

[Patent Literature 1] Unexamined Japanese Patent Application KOKAIPublication No.2002-261727

[Patent Literature 2] Unexamined Japanese Patent Application KOKAIPublication No.2001-320344

[Patent Literature 3] Unexamined Japanese Patent Application KOKAIPublication No. 2001-36445

[Non-Patent Literature 1] Chang-Jun AHN and Iwao SASASE, ConvolutionalCoded Coheretn and Differential Unitary Space-Time Modulated OFDM withBit Interleaving for Multiple Antenna System, technical report of IEICE,TECHNICAL REPORT OF IEICE, SST2002-47, October 2002, pp. 75-80

Patent Literature 1 discloses an invention relating to a multi-carriersignal transmitter apparatus used in digital wireless communications.

Particularly, the literature discloses an OFDM signal transmitterapparatus which is designed to supply a same single local oscillationsignal output from a single local oscillator to a plurality oftransmitter side frequency converters corresponding to a plurality ofantennas respectively, and which can realize high-speed transmission byimproving frequency utilization efficiency while maintaining theorthogonality of the carriers in the plurality of antennas.

Patent Literature 2 discloses an invention relating to channelestimation by clustered OFDM receiver apparatuses.

Particularly, the literature discloses an invention which suppliessignals having come to one or more antennas through respectivetransmission channels to corresponding FFT elements, filters the outputsfrom the FFT elements, combines the filtered signals, and supplies thecombined signal to a threshold element, and which uses a unique matrixof a frequency-domain correlation matrix of each channel as the optimumchannel estimator, wherein the matrix is dependent on the delay profileof each channel.

Patent Literature 3 discloses an invention relating to a diversityreceiving device for mobile transmitter apparatus, which performsbandwidth-division diversity reception by using a plurality of receivedsignals having the same frequency, and employs simultaneous FFT, therebyto reduce the size of the apparatus and improve its mobility.

Particularly, the literature discloses a diversity receiving devicewhich requires no more than one cable, and has an FFT means forobtaining frequency axis data by fast Fourier transform, and aselecting/combining output means for calculating differences betweensymbols of the frequency axis data and selecting or combiningdifferentially demodulated carrier data of OFDM signals obtained by thedifference calculation to output the selected or combined data.

Non-Patent Literature 1 is a paper of a past study joined by one of theinventors listed in the present application, and discloses an inventionwhich performs space-time modulation/demodulation by a unitary matrix,and transmits signals at different times with the use of a plurality ofantennas.

Notwithstanding these techniques, various other communication techniquesapplicable to OFDM communications are strongly demanded.

The present invention was made to solve the above-described problem, andan object of the present invention is to provide a transmitterapparatus, a receiver apparatus, a transmitting method, and a receivingmethod for performing efficient communication by usingmodulation/demodulation by a unitary matrix in which components otherthan the diagonal components are 0, and a program for realizing these ona computer.

DISCLOSURE OF THE INVENTION

To achieve the above object, the following invention is disclosed inaccordance with the principle of the present invention.

A transmitter apparatus according to a first aspect of the presentinvention comprises a serial-parallel converter, a unitary matrixmodulator, a splitter, an inverse Fourier transform unit, aparallel-serial converter, and a transmission unit, and is structured asfollows.

The serial-parallel converter receives an input of a signal to betransmitted, and serial-parallel-converts the signal to output m (m≧2)number of intermediate signals.

The unitary matrix modulator modulates the output m number ofintermediate signals into a unitary matrix having m rows and m columnswhose components other than whose diagonal components are 0, and outputsthe obtained matrix.

The splitter supplies the respective diagonal components of the outputmatrix to input channels of the inverse Fourier transform unit as inputsignals.

The inverse Fourier transform unit outputs m number ofinverse-Fourier-transformed signals obtained by performing inverseFourier transform of the input signals supplied to the input channels.

The parallel-serial converter parallel-serial-converts the output mnumber of inverse-Fourier-transformed signals to output one transmissionsignal.

The transmission unit transmits the output transmission signal.

The difference between the frequencies of any two of the channels of theinverse Fourier transform unit is equal to or larger than apredetermined coherent bandwidth.

A receiver apparatus according to another aspect of the presentinvention comprises a reception unit, a serial-parallel converter, aFourier transform unit, an inverse splitter, a unitary matrixdemodulator, and a parallel-serial converter, and is structured asfollows.

The reception unit receives a transmission signal having beentransmitted, and outputs this as a reception signal.

The serial-parallel converter serial-parallel-converts the outputreception signal to output m (m≧2) number of intermediate signals.

The Fourier transform unit outputs m number of Fourier-transformedsignals obtained by performing Fourier transform of the output m numberof intermediate signals.

The inverse splitter supplies the output m number of Fourier-transformedsignals to the unitary matrix demodulator.

The unitary matrix demodulator demodulates a unitary matrix having mrows and m columns whose components other than whose diagonal componentsare 0, from a matrix having m rows and m columns in which each of thesupplied m number of Fourier-transformed signals are its diagonalcomponent and components other than the diagonal components are 0.

The parallel-serial converter parallel-serial-converts the demodulatedplurality of demodulated signals, and outputs them as a signal havingbeen transmitted.

The difference between the frequencies of any two of channels of theFourier transform unit is equal to or larger than a predeterminedcoherent bandwidth.

A transmitting method according to another aspect of the presentinvention comprises a serial-parallel converting step, a unitary matrixmodulating step, a splitting step, an inverse Fourier transforming step,a parallel-serial converting step, and a transmitting step, and isconfigured as follows.

At the serial-parallel converting step, an input of a signal to betransmitted is received and the signal is serial-parallel-converted tooutput m (m≧2) number of intermediate signals.

At the unitary matrix modulating step, the output m number ofintermediate signals are modulated into a unitary matrix having m rowsand m columns whose components other than whose diagonal components are0, and the obtained matrix is output.

At the splitting step, the respective diagonal components of the outputmatrix are supplied to input channels of inverse Fourier transform asinput signals.

At the inverse Fourier transforming step, m number ofinverse-Fourier-transformed signals are output, which are obtained byperforming inverse Fourier transform of the input signals supplied tothe input channels of inverse Fourier transform.

At the parallel-serial converting step, the output m number ofinverse-Fourier-transformed signals are parallel-serial-converted tooutput one transmission signal.

At the transmitting step, the output transmission signal is transmitted.The difference between the frequencies of any two of the channels ofinverse Fourier transform at the inverse Fourier transforming step isequal to or larger than a predetermined coherent bandwidth.

A receiving method according to another aspect of the present inventioncomprises a receiving step, a serial-parallel converting step, a Fouriertransforming step, an inverse splitting step, a unitary matrixdemodulating step, and a parallel-serial converting step, and isconfigured as follows.

At the receiving step, a transmission signal having been transmitted isreceived and output as a reception signal.

At the serial-parallel converting step, the output reception signal isserial-parallel-converted to output m (m≧2) number of intermediatesignals.

At the Fourier transforming step, m number of Fourier-transformedsignals are output, which are obtained by performing Fourier transformof the output m number of intermediate signals.

At the inverse splitting step, the output m number ofFourier-transformed signals are supplied to the unitary matrixdemodulating step.

At the unitary matrix demodulating step, a unitary matrix having m rowsand m columns whose components other than whose diagonal components are0 is demodulated from a matrix having m rows and m columns in which eachof the supplied m number of Fourier-transformed signals is its diagonalcomponent and components other than the diagonal components are 0.

At the parallel-serial converting step, the demodulated plurality ofdemodulated signals are parallel-serial-converted, to output them as asignal having been transmitted.

The difference between the frequencies of any two of channels of Fouriertransform at the Fourier transforming step is equal to or larger than apredetermined coherent bandwidth.

A transmitter apparatus according to another aspect of the presentinvention comprises a serial-parallel converter, a plurality of unitarymatrix modulators, a splitter, an inverse Fourier transform unit, aparallel-serial converter, and a transmission unit, and is structured asfollows.

The serial-parallel converter receives an input of a signal to betransmitted, and serial-parallel-converts the signal to output m×n (m≧2,n≧1) number of intermediate signals.

The plurality of unitary matrix modulators each modulate any m number ofsignals of the output m×n number of intermediate signals, with nodoubles, into a unitary matrix having m rows and m columns whosecomponents other than whose diagonal components are 0, and output theobtained matrix.

The splitter supplies the respective diagonal components of the outputmatrix to input channels of the inverse Fourier transform unit as inputchannels.

The inverse Fourier transform unit outputs m number ofinverse-Fourier-transformed signals obtained by performing inverseFourier transform of the input signals supplied to the input channelsthereof.

The parallel-serial converter parallel-serial-converts the output mnumber of inverse-Fourier-transformed signals to output one transmissionsignal.

The transmission unit transmits the output transmission signal.

Among any two channels of the inverse Fourier transform unit, any twochannels to which the diagonal components of the matrix output from theplurality of unitary matrix modulators are supplied have therebetween afrequency difference which is equal to or larger than a predeterminedcoherent bandwidth.

The transmitter apparatus of the present invention may be structuredsuch that a diagonal component on a j-th row and a j-th column of amatrix output from an i-th one of he plurality of unitary matrixmodulators (where 0≦i≦n, 0≦j≦m) is supplied to a j×m+i-th input channelof the inverse Fourier transform unit.

A receiver apparatus according to another aspect of the presentinvention comprises a reception unit, a serial-parallel converter, aFourier transform unit, an inverse splitter, a plurality of unitarymatrix demodulators, and a parallel-serial converter, and is structuredas follows.

The reception unit receives a transmission signal having beentransmitted, and outputs this as a reception signal.

The serial-parallel converter serial-parallel-converts the outputreception signal to output m×n (m≧2, n≧1) number of intermediatesignals.

The Fourier transform unit outputs m×n number of Fourier-transformedsignals obtained by performing Fourier-transform of the output m×nnumber of intermediate signals.

The inverse splitter supplies n number of signals of the output m×nnumber of Fourier-transformed signals to each of the unitary matrixdemodulators with no doubles.

Each of the plurality of unitary matrix demodulators demodulates aunitary matrix having m rows and m columns whose components other thanwhose diagonal components are 0, from a matrix having m rows and mcolumns in which each of the supplied m number of Fourier-transformedsignals is its diagonal component and components other than the diagonalcomponents are 0.

The parallel-serial converter parallel-serial-converts the plurality ofdemodulated signals having been demodulated, and outputs them as signalshaving been transmitted.

Among any two channels of the Fourier transform unit, any two channelsthat are to output Fourier-transformed signals to be supplied to each ofthe plurality of unitary matrix demodulators have therebetween afrequency difference which is equal to or larger than a predeterminedcoherent bandwidth.

The receiver apparatus according to the present invention may bestructured such that each of the plurality of unitary matrixdemodulators compares each of a plurality of predetermined unitarymatrices which each have m rows and m columns and whose components otherthan whose diagonal components are 0, with a matrix having m rows and mcolumns in which each of the supplied m number of Fourier-transformedsignals is its diagonal component and components other than the diagonalcomponents are 0, selects one of the plurality of predetermined unitarymatrices that has a smallest Euclidean distance, and obtains theselected one as a demodulation result.

The receiver apparatus according to the present invention may bestructured such that a diagonal component on a j-th row and a j-thcolumn of the matrix compared by an i-th one of the plurality of unitarymatrix demodulators (where 0≦i<n, 0≦j<m) is one that has been outputfrom a j×m+i-th output channel of the inverse Fourier transform unit.

A program according to another aspect of the present invention isconfigured to control a computer to function as each unit of theabove-described transmitter apparatus.

A program according to another aspect of the present invention isconfigured to control a computer to function as each unit of theabove-described receiver apparatus.

The transmitter apparatus, the receiver apparatus, the transmittingmethod, and the receiving method of the present invention can berealized by the programs of the present invention being executed by acomputer capable of communicating with other devices.

Further, an information recording medium storing the programs of thepresent invention may be distributed or sold independently from thecomputer. Furthermore, the programs of the present invention may betransmitted, distributed, and sold via a computer communication networksuch as the Internet, etc.

Particularly, in a case where the computer includes a programmableelectronic circuit such as a DSP (Digital Signal Processor), an FPGA(Field Programmable Gate Array), etc., a software radio type methodwhich would realize the transmitter apparatus and receiver apparatus ofthe present invention becomes available, if the programs of the presentinvention stored on an information recording medium are transmitted tothe computer so that the DSP or FPGA in the computer may execute theprograms.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exemplary diagram of a transmitter apparatus which performsthe simplest unitary matrix modulation;

FIG. 2 is an exemplary diagram showing a rough structure of atransmitter apparatus in which an OFDM technique and unitary matrixmodulation are combined;

FIG. 3 is an explanatory diagram showing an explanation of a splittingprocess;

FIG. 4 is an exemplary diagram showing a rough structure of a receiverapparatus which is paired with the transmitter apparatus shown in FIG.2;

FIG. 5 is an exemplary diagram showing a rough structure of atransmitter apparatus according to another embodiment;

FIG. 6 is an exemplary diagram showing a rough structure of a receiverapparatus according to another embodiment; and

FIGS. 7 are exemplary diagrams showing rough schemes of a splittingprocess according to another embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

The best embodiment for carrying out the present invention will bedescribed below. However, the present embodiment is intended forillustration, and other embodiments that re under the principle of thepresent invention will thus also be included in the scope of he presentinvention.

First, a unitary matrix to be used in the present embodiment will bedescribed. As for a square matrix S having m rows and m columns (itscomponent on the i-th row and j-th column being expressed as s_(i,j))and its adjoint matrix (conjugate transpose matrix) S* (its component onthe i-th row and j-th column being s_(i,j)*, where x* being a conjugatecomplex number of x), in a case whereSS*=S*S=Eis established, where E is an identity matrix having m rows and mcolumns, S is said to be a “unitary matrix”. According to the presentembodiment, a unitary matrix whose components other than the diagonalcomponents are all 0 will be used.

For example, as a unitary matrix having 2 rows and 2 columns, the oneshown below is conceivable. $\begin{matrix}\begin{pmatrix}1 & 0 \\0 & 1\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 1} \rbrack \\\begin{pmatrix}i & 0 \\0 & i\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 2} \rbrack \\\begin{pmatrix}{- 1} & 0 \\0 & {- 1}\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 3} \rbrack \\\begin{pmatrix}{- i} & 0 \\0 & {- i}\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 4} \rbrack\end{matrix}$

In order to decide what matrix to select as a unitary matrix having mrows and m columns whose components other than the diagonal componentsare 0, a technique similar to that disclosed in [Non-Patent Literature1] can be employed.

In the explanation example below, those four kinds of unitary matricesabove will be employed for modulation/demodulation. Since it being 4=2²,2-bit information can be associated with these unitary matrices inone-to-one correspondence.

Hence, 2-bit inputs as shown below are associated with these,respectively. $\begin{matrix}\begin{pmatrix}0 \\0\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 5} \rbrack \\\begin{pmatrix}1 \\0\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 6} \rbrack \\\begin{pmatrix}0 \\1\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 7} \rbrack \\\begin{pmatrix}1 \\1\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 8} \rbrack\end{matrix}$

Modulation/demodulation by a unitary matrix of two rows and two columnswill be explained based on these examples. That is, in a case where twosignals represented by [Mathematical Expression 5] to [MathematicalExpression 8] (the values of the respective components eachcorresponding to one signal) are input, to be output by unitary matrixmodulation as a modulation result is a matrix represented by[Mathematical Expression 1] to [Mathematical Expression 4] that isassociated with the two signals. The reverse of this operation is doneby unitary matrix demodulation.

(Basic Unitary Matrix Modulation)

FIG. 1 is a block diagram of a transmitter apparatus which performs thesimplest unitary matrix modulation. The following explanation will begiven with reference to this drawing.

In the transmitter apparatus 1, a signal to be transmitted is input to aserial-parallel converter 102 at a rate of f bits per unit time.

The serial-parallel converter 102 serial-parallel-converts the signalinto two intermediate signals. Hence, the output rate of eachintermediate signal is f/2 per unit time.

Next, these intermediate signals are supplied to a unitary matrixmodulator 103. The unitary matrix modulator 103 receives the input ofthe two intermediate signals and outputs two modulated signals. In thiscase, with the input two intermediate signals seen as a vertical vector([Mathematical Expression 5] to [Mathematical Expression 8]), theunitary matrix modulator 103 outputs a matrix ([Mathematical Expression1] to [Mathematical Expression 4]) that is associated with the verticalvector.

For example, in a case where the two intermediate signals are those thatare represented by [Mathematical Expression 5] and the matrix thatshould be output is one that is represented by [Mathematical Expression1], “1, 0” is output as one of the modulated signals and “0, 1” isoutput as the other in the time order. Thus, the output rate of eachmodulated signal is f per unit time.

Then, respective superimposing units 104 superimpose the modulatedsignals on carrier waves having different carrier frequencies from eachother. The values of the respective components of the unitary matrix aregenerally complex numbers, thus changing the phase of the results ofsuperimposition. Respective antennas 5 output the corresponding signals.

As described above, the components of the unitary matrix output by theunitary matrix modulator 105 other than its diagonal components are 0.Accordingly, in the above-described example, when any of the antennas105 outputs a signal (when the transmission power is not 0), none of theother antennas 105 outputs a signal (the transmission power is 0). Inthis manner, one signal is transmitted while being extended on a timeaxis and a space axis respectively.

Here, taking advantage of that the antennas 105 output signals mutuallyexclusively, i.e., the diagonal components of the unitary matrix outputby the unitary matrix modulator 103 are all 0, compression on the timeaxis will be considered. Further to consider is to manage with only oneantenna 105, as the embodiment shown in FIG. 1 indicates that therequired number of antennas 105 is equal to the number of dimensions ofthe unitary matrix. The technique to be used therefor is the OFDMtechnique.

Embodiment of Transmitter Apparatus

FIG. 2 shows a rough structure of a transmitter apparatus in which theOFDM technique and unitary matrix modulation are combined. In thetransmitter apparatus 101, the processes of the serial-parallelconverter 102 and unitary matrix modulator 103 are the same as theembodiment shown in FIG. 1.

That is, when a signal to be transmitted is input to the serial-parallelconverter 102, the serial-parallel converter 102serial-parallel-converts the signal into two intermediate signals.

Next, these intermediate signals are supplied to the unitary matrixmodulator 103. The unitary matrix modulator 103 receives the input ofthe two intermediate signals and outputs two modulated signals. In thiscase, with the input two intermediate signals seen as a vertical vector([Mathematical Expression 5] to [Mathematical Expression 8]), theunitary matrix modulator 103 outputs a matrix ([Mathematical Expression1] to [Mathematical Expression 4]) that is associated with the verticalvector.

For example, in a case where the two intermediate signals are those thatare represented by [Mathematical Expression 6] and the matrix thatshould be output is one that is represented by [Mathematical Expression2], “i, 0” is output as one of the modulated signals and “0, i” isoutput as the other in the time order.

Then, a splitter 111 inputs combinations of the real part and imaginarypart of those signals output from the unitary matrix modulator 103 (thecombinations corresponding to the number of dimensions of the matrix) tocombinations (I channel and Q channel) of the real part and imaginarypart of an inverse Fourier transform unit 112 respectively, so thatinverse Fourier transform will be applied thereon.

FIG. 3 explains the process of the splitter 111. As for an i-th signal,the splitter 111 outputs the value of the component on the i-th row andi-th column of the matrix. That is, in the above-described example, thesplitter 111 outputs [Mathematical Expression 9]. $\begin{matrix}\begin{pmatrix}i \\i\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 9} \rbrack\end{matrix}$

Since all the components other than the component (diagonal component)on the i-th row and i-th column are 0, the information will not be losteven if such a process is performed. The splitter may interchange theoutputs. When the splitting process is completed, the outputs aresupplied to the inverse Fourier transform unit 112.

An embodiment in which the unitary matrix modulator 103 does not outputa unitary matrix itself, but outputs the diagonal components of aunitary matrix may be employed. In this case, if the signal interchangeby the splitter 111 is not performed, the splitter 111 becomesunnecessary and the outputs of the unitary matrix modulator 103 aredirectly supplied to the inverse Fourier transform unit 112. This meansthat in the present example, the vectors of the following [MathematicalExpression 10] to [Mathematical Expression 13] will be used instead of[Mathematical Expression 1] to [Mathematical Expression 4].$\begin{matrix}\begin{pmatrix}1 \\1\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 10} \rbrack \\\begin{pmatrix}i \\i\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 11} \rbrack \\\begin{pmatrix}{- 1} \\{- 1}\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 12} \rbrack \\\begin{pmatrix}{- i} \\{- i}\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 13} \rbrack\end{matrix}$

The inverse Fourier transform unit 112 performs inverse Fouriertransform of the input signals in the same manner as in the ordinaryOFDM communication. It is desired that the difference between thefrequencies of the channels of inverse Fourier transform (the channelscorresponding to sub-carriers of OFDM communication) performed by theinverse Fourier transform unit 112 be equal to or larger than apredetermined coherent bandwidth. A coherent bandwidth is a differencebetween the frequencies of channels through which a delayed wave willresult in similar channel responses to each other. The longer the delaytime of a delayed wave is, the narrower the coherent bandwidth of achannel is, whereas the shorter the delay time of a delayed wave is, thewider the coherent bandwidth of a channel is.

When considering an OFDM system for, for example, 128 sub-carriers in abandwidth of 80 MHz, the bandwidth Δf of a sub-carrier is Δf=80MHz/128=625 kHz. Here, if it is assumed that RMS (Root Mead Squared)delay spread τ=714 ns, the coherent bandwidth B_(c) will be B_(c)=1/(50τ)=28 kHz t 0.048 Δf The constant 50 in this equation is a calculationcoefficient for the coherent bandwidth, and is a constant similar to aso-called safety coefficient.

Accordingly, in such a case, the difference between the frequencies ofadjoining channels (sub-carriers) is sufficiently larger than thecoherent bandwidth. Like this example, if the size of the RMS delayspread can be known from the condition of a propagation transmissionpath and the condition of the frequency band used, etc., the coherentbandwidth can be calculated from that size of the spread.

When the inverse Fourier transform is completed, the output signals areparallel-serial-converted by a parallel-serial converter 113 into asingle signal, and a transmission unit 114 transmits the signal from oneantenna 105. This stage is the same as the ordinary OFDM transmission.

Embodiment of Receiver Apparatus

FIG. 4 is an exemplary diagram showing a rough structure of a receiverapparatus, which will serve in pair with the transmitter apparatus 101shown in FIG. 2. The following explanation will be given with referenceto this drawing.

A reception unit 403 of the receiver apparatus 401 receives the signaltransmitted from the transmitter apparatus 101 via an antenna 402. Next,a serial-parallel converter 404 serial-parallel-converts this receivedsignal to output 2 intermediate signals. This value “2” is based on thatthe unitary matrix modulation used by the transmitter apparatus 101 usesa unitary matrix of 2 rows and 2 columns, hence m number of intermediatesignals will be output in a case where a unitary matrix of m rows and mcolumns is used.

Then, a Fourier transform unit 405 performs Fourier transform of theintermediate signals likewise in the ordinary OFDM communication, tooutput 2 Fourier-transformed signals. The Fourier transform unit 405 ispaired with the inverse Fourier transform unit 111 of the transmitterapparatus 101, and the difference between the frequencies of channels(sub-carriers) (the difference being the bandwidth of each channel(sub-carrier)) is equal to or larger than the coherent bandwidth, asdescribed above.

Without various influences on the radio transmission path, the signalsto be output here should be (proportional to) any of [MathematicalExpression 10] to [Mathematical Expression 13]. In reality, however,gaps from these signals are produced due to the influences on the radiotransmission path.

Hence, an inverse splitter 406 determines to which of [MathematicalExpression 10] to [Mathematical Expression 13] the Fourier-transformedsignals are the closest, to obtain a vector determined as the closest.The “closeness” is typically determined by the Euclidean distancebetween the vectors. However, various methods for calculating the“distance” may be employed, such as the total sum of the absolute valuesof the differences between the respective components of the vectors,etc.

Then, a unitary matrix is obtained, whose diagonal components are thecomponents of the vector having been obtained through “inversesplitting”, which is the inverse conversion of the splitting shown inFIG. 3.

A unitary matrix demodulator 407 outputs a vector ([MathematicalExpression 1] to [Mathematical Expression 4] in the above-describedexample) that is pre-associated with the unitary matrix output by theinverse splitter.

Further, a parallel-serial converter 408 parallel-serial-converts thevector output by the unitary matrix demodulator 407 and outputs it.

An existing electronic element circuit for fast Fourier transform can beused as the inverse Fourier transform unit 112 and the Fourier transformunit 405. However, in this case, the bandwidth of each channel(sub-carrier) is generally fixed. Hence, in a case where the bandwidthis narrower than the coherent bandwidth calculated in theabove-described manner, it may be possible to broaden the differencebetween the frequencies of the frequency bands of the channels by usingthe channels by skipping some channels at predetermined intervals.

Other Embodiments

In the above-described embodiment, only one unitary matrix modulator andonly one unitary matrix demodulator are employed to perform modulationand demodulation. According to the present embodiment, n number ofunitary matrix modulators and unitary matrix demodulators respectively,each having m rows and m columns, are used, and m×n number of channelsare used in OFDM. Typically, it is set that m=2, as is set so in theabove-described embodiment.

FIG. 5 and FIG. 6 are explanatory diagrams showing a rough structure ofa transmitter apparatus according to the present embodiment and a roughstructure of a receiver apparatus according to the present embodiment,respectively. The components same as those in the above-describedembodiment are given the same reference numerals.

In the transmitter apparatus 101, the serial-parallel converter 102receives an input of a signal to be transmitted, andserial-parallel-converts the signal to output m×n (m≧2, n≧1) number ofintermediate signals. These intermediate signals are denoted as a₀, a₁,. . . , a_(m×n−1), sequentially.

The plurality of unitary matrix modulators 103 each modulate any mnumber of intermediate signals of the output m×n number of intermediatesignals with no double-taking of the signals, into unitary matrices of mrows and m columns in which components other than the diagonalcomponents are 0, and output the obtained matrices.

To assign numerals 0 to n−1 to the respective unitary matrix modulators103, the i-th unitary matrix modulator 103 typically takes theintermediate signals a_(i×m), a_(i×m+1), . . . , a_(i×m+m−1).

Hereinafter, to facilitate the understanding, the diagonal component onthe j-th row and j-th column of the matrix output by the i-th unitarymatrix modulator 103 is denoted as r_(i,j).

Then, the splitter 104 supplies each of the diagonal components of theoutput matrices to the input channel of the inverse Fourier transformunit 105 as an input signal. At this time, it is desired that thediagonal components r_(i,0), r_(i,1), . . . , r_(i,m−1), . . . , whichare output from the same unitary matrix modulator 103 be supplied to theinput channels having frequencies distanced from each other as much aspossible. Further, at this time, the difference between the frequenciesshould be equal to or larger than the coherent bandwidth.

This condition is a more relaxed one than in the above-describedembodiment. That is, according to the above-described embodiment, it isrequired that for all the combinations of input channels, the differencebetween their frequencies be equal to or larger than the coherentbandwidth. According to the present embodiment, it is sufficient if forthe input channels to which diagonal components output from the sameunitary matrix modulator 103 are to be supplied, the difference betweentheir frequencies is equal to or larger than the coherent bandwidth.

The condition can be set so because signals (diagonal components) outputfrom the same unitary matrix modulator 103 are similar in their channelresponse.

Needless to say, in the present embodiment as well, it is desirable as acure for delayed waves that the difference between the frequencies islarge for all the input channels. However, since being in the trade-offrelation with the performance, these values may be adaptively set inaccordance with the field of application.

Here, assume that the input channels of the inverse Fourier transformunit 105 are named c₀, c₁, . . . , c_(m×n−1) in the order of theirfrequencies. In order for the diagonal components r_(i,0), r_(i,1), . .. , r_(i,m−1), . . . , output from the same unitary matrix modulator 103to be supplied to the input channels having frequencies distanced asmuch as possible, the diagonal component r_(i,j) should be supplied tothe input channel c_(j×m+1). Such a method of supplying signals is shownin FIG. 7(a).

Other that this, a diagonal component r_(i,j) may be supplied toc_(j×(m+k)+i), where k is a predetermined constant equal to or largerthan 1. This is shown in FIG. 7(b). In this case, among the inputchannels of the inverse Fourier transform unit 105, some of them(channels corresponding to c_(j×(m+k)+i+1) to c_(j×(m+k)+i+k−1)) are notsupplied with the outputs from the unitary matrix modulators 105. Thus,typically, the value 0 will be supplied thereto. However, these inputchannels may be supplied with known signals, so that these channels maybe used for transmitting pilot signals. In this case, the receiverapparatus 401 can have additional processes such as signal compensationof various kinds, by synchronizing with the pilot signals.

Then, the inverse Fourier transform unit 105 outputs a plurality ofinverse-Fourier-transformed signals obtained by performing inverseFourier transform of the input signals supplied to the input channelsthereof.

The parallel-serial converter 106 parallel-serial-converts the outputplurality of inverse-Fourier-transformed signals to output onetransmission signal.

The transmission unit 107 transmits the output transmission signal.

On the other hand, the receiver apparatus 401 counter to the transmitterapparatus 101 comprises a reception unit 403, a serial-parallelconverter 404, a Fourier transform unit 405, an inverse splitter 406, aplurality of unitary matrix demodulators 407, and a parallel-serialconverter 408, and is structured as follows.

The reception unit 403 receives the transmission signal as transmitted,via the antenna 402, and outputs it as a reception signal.

The serial-parallel converter 404 serial-parallel converts the outputreception signal to output m×n (m≧2, n≧1) number of intermediatesignals.

Further, the Fourier transform unit 405 outputs m×n number ofFourier-transformed signals obtained by performing Fourier transform ofthe output m×n number of intermediate signals.

Then, the inverse splitter 406 supplies the output m×n number ofFourier-transformed signals to the unitary matrix demodulators 407, withn number of signals supplied to each, with no doubles. Thecorrespondence here is reverse to that in the transmitter apparatus 101.To describe it with reference to the examples shown in FIGS. 7, theinverse splitting process is obtained by reversing the arrows indicatingthe directions in which the signals are supplied.

Each of the plurality of unitary matrix demodulators 407 demodulates aunitary matrix of m rows and m columns whose components other than thediagonal components are 0, from a matrix of m rows and m columns inwhich each of the supplied m number of Fourier-transformed signals isits diagonal component and the components other than the diagonalcomponents are 0. That is, likewise in the above-described embodiment,the unitary matrix demodulator 407 selects one of “predetermined unitarymatrices” that has the smallest Euclidean distance from “the matrix of mrows and m columns in which each of the Fourier-transformed signals isits diagonal component and the components other than the diagonalcomponents are 0”, i.e., one of “vectors each made up of the diagonalcomponents of any of the predetermined unitary matrices” that has thesmallest Euclidean distance from “the vector whose components are therespective Fourier-transformed signals”, and outputs the signal which isassociated with the selected vector as the demodulated signal.

For example, in a case where [Mathematical Expression 14] shown below is“the matrix of m rows and m columns in which each of theFourier-transformed signals is its diagonal component and the componentsother than the diagonal components are 0”, the one among [MathematicalExpression 1] to [Mathematical Expression 4] that is the closest to thismatrix in terms of the Euclidean distance is the unitary matrixrepresented by [Mathematical Expression 1]. Thus, the demodulated signalis [Mathematical Expression 5]. $\begin{matrix}\begin{pmatrix}0.8 & 0 \\0 & 0.9\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 14} \rbrack\end{matrix}$

Before the Euclidean distance is calculated, “the matrix of m rows and mcolumns in which each of the Fourier-transformed signals is its diagonalcomponent and the components other than the diagonal components are 0”may be appropriately normalized. For example, a conceivable method is todivide each diagonal component by “the root mean of the diagonalcomponents”. In this case, to calculate the normalized matrixcorresponding to [Mathematical Expression 14], [Mathematical Expression15] is obtained, since the root mean of the diagonal components is0.85147. $\begin{matrix}\begin{pmatrix}0.93955 & 0 \\0 & 1.05700\end{pmatrix} & \lbrack {{Mathematical}\quad{Expression}\quad 15} \rbrack\end{matrix}$

Then, the parallel-serial converter 407 parallel-serial-converts theplurality of demodulated signals as demodulated, and outputs them as thesignals having been transmitted.

As regards the selection of a unitary matrix whose components other thanthe diagonal components are 0, and the association between a signal anda unitary matrix in he transmitter apparatus 101 and receiver apparatus401, a selection and association that re common among the respective“pairs of unitary matrix modulators 103 and their corresponding unitarymatrix demodulators 407” may be employed for each pair, or selectionsand associations varied among the pairs may be employed. Particularly,for adjoining “unitary matrix modulators 103 and their correspondingunitary matrix demodulators 407”, varied selections and associations ofthe unitary matrix may be employed.

The performance of the communication by these transmitter apparatus andreceiver apparatus under the environment of the Doppler frequency of 10Hz was calculated by computer simulation. In case of employing splittingof 98 samples, the BER (Bit Error Rate) was improved by as much as 10⁻²at Eb/No of 5 db as compared with earlier OFDM communications, provingthe effectiveness of the present technique.

With the techniques of software radio, etc., these transmitter apparatusand receiver apparatus can be realized by providing software to variouskinds of computers, FPGA (Field Programmable Gate Array), and DSP(Digital Signal Processor).

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide atransmitter apparatus, a receiver apparatus, a transmitting method, anda receiving method for performing efficient communication by usingmodulation/demodulation by a unitary matrix in which components otherthan the diagonal components are 0, and a program for realizing these ona computer.

1. A transmitter apparatus, comprising a serial-parallel converter, aunitary matrix modulator, a splitter, an inverse Fourier transform unit,a parallel-serial converter, and a transmission unit, wherein: saidserial-parallel converter receives an input of a signal to betransmitted, and serial-parallel-converts the signal to output m (m≧2)number of intermediate signals; said unitary matrix modulator modulatesthe output m number of intermediate signals into a unitary matrix havingm rows and m columns whose components other than whose diagonalcomponents are 0, and outputs the obtained matrix; said splittersupplies the respective diagonal components of the output matrix toinput channels of said inverse Fourier transform unit as input signals;said inverse Fourier transform unit outputs m number ofinverse-Fourier-transformed signals obtained by performing inverseFourier transform of the input signals supplied to the input channels;said parallel-serial converter parallel-serial-converts the output mnumber of inverse-Fourier-transformed signals to output one transmissionsignal; and said transmission unit transmits the output transmissionsignal, and wherein a difference between frequencies of any two of thechannels of said inverse Fourier transform unit is equal to or largerthan a predetermined coherent bandwidth.
 2. A receiver apparatus,comprising a reception unit, a serial-parallel converter, a Fouriertransform unit, an inverse splitter, a unitary matrix demodulator, and aparallel-serial converter, wherein: said reception unit receives atransmission signal having been transmitted, and outputs this as areception signal; said serial-parallel converterserial-parallel-converts the output reception signal to output m (m≧2)number of intermediate signals; said Fourier transform unit outputs mnumber of Fourier-transformed signals obtained by performing Fouriertransform of the output m number of intermediate signals; said inversesplitter supplies the output m number of Fourier-transformed signals toaid unitary matrix demodulator; said unitary matrix demodulatordemodulates a signal associated with a unitary matrix having m rows andm columns whose components other than whose diagonal components are 0,from a matrix having m rows and m columns in which each of the suppliedm number of Fourier-transformed signals are its diagonal component andcomponents other than the diagonal components are 0, and outputs thesignal as a demodulated signal; and said parallel-serial converterparallel-serial-converts the demodulated plurality of demodulatedsignals, and outputs them as a signal having been transmitted, andwherein a difference between frequencies of any two of channels of saidFourier transform unit is equal to or larger than a predeterminedcoherent bandwidth.
 3. A transmitting method, comprising aserial-parallel converting step, a unitary matrix modulating step, asplitting step, an inverse Fourier transforming step, a parallel-serialconverting step, and a transmitting step, wherein: at saidserial-parallel converting step, an input of a signal to be transmittedis received and the signal is serial-parallel-converted to output m(m>2) number of intermediate signals; at said unitary matrix modulatingstep, the output m number of intermediate signals are modulated into aunitary matrix having m rows and m columns whose components other thanwhose diagonal components are 0, and the obtained matrix is output; atsaid splitting step, the respective diagonal components of the outputmatrix are supplied to input channels of inverse Fourier transform asinput signals; at said inverse Fourier transforming step, m number ofinverse-Fourier-transformed signals are output, which are obtained byperforming inverse Fourier transform of the input signals supplied tothe input channels of inverse Fourier transform; at said parallel-serialconverting step, the output m number of inverse-Fourier-transformedsignals are parallel-serial-converted to output one transmission signal;and at said transmitting step, the output transmission signal istransmitted, and wherein a difference between frequencies of any two ofthe channels of inverse courier transform at said inverse Fouriertransforming step is equal to or larger than a redetermined coherentbandwidth.
 4. A receiving method, comprising a receiving step, aserial-parallel converting step, a Fourier transforming step, an inversesplitting step, a unitary matrix demodulating step, and aparallel-serial converting step, wherein: at said receiving step, atransmission signal having been transmitted is received and output as areception signal; at said serial-parallel converting step, the outputreception signal is serial-parallel-converted to output m (m>2) numberof intermediate signals; at said Fourier transforming step, m number ofFourier-transformed signals are output, which are obtained by performingFourier transform of the output m number of intermediate signals; atsaid inverse splitting step, the output m number of Fourier-transformedsignals are supplied to said unitary matrix demodulating step; at saidunitary matrix demodulating step, a signal associated with a unitarymatrix having m rows and m columns whose components other than whosediagonal components are 0 is demodulated from a matrix having m rows andm columns in which each of the supplied m number of Fourier-transformedsignals is its diagonal component and components other than the diagonalcomponents are 0, and this signal is output as a demodulated signal; andat said parallel-serial converting step, the demodulated plurality ofdemodulated signals are parallel-serial-converted, to output them as asignal having been transmitted, and wherein a difference betweenfrequencies of any two of channels of Fourier transform at said Fouriertransforming step is equal to or larger than a predetermined coherentbandwidth.
 5. A program for controlling a computer to function as aserial-parallel converter, a unitary matrix modulator, a splitter, aninverse Fourier transform unit, a parallel-serial converter, and atransmission unit, wherein in said computer, said program controls: saidserial-parallel converter to receive an input of a signal to betransmitted and serial-parallel-convert the signal to output m (m≧2)number of intermediate signals; said unitary matrix modulator tomodulate the output m number of intermediate signals into a unitarymatrix having m rows and m columns whose components other than whosediagonal components are 0 and output the obtained matrix; said splitterto supply the respective diagonal components of the output matrix toinput channels of said inverse Fourier transform unit as input signals;said inverse Fourier transform unit to output m number ofinverse-Fourier-transformed signals obtained by performing inverseFourier transform of the input signals supplied to the input channelsthereof; said parallel-serial converter to parallel-serial-convert theoutput m number of inverse-Fourier-transformed signals to output onetransmission signal; and said transmission unit to transmit the outputtransmission signal, and wherein a difference between frequencies of anytwo of the channels of said inverse Fourier transform unit is equal toor larger than a predetermined coherent bandwidth.
 6. A program forcontrolling a computer to function as a reception unit, aserial-parallel converter, a Fourier transform unit, an inversesplitter, a unitary matrix demodulator, and a parallel-serial converter,wherein in said computer, said program controls: said reception unit toreceive a transmission signal having been transmitted and output this asa reception signal; said serial-parallel converter toserial-parallel-convert the output reception signal to output m (m≧2)number of intermediate signals; said Fourier transform unit to output mnumber of Fourier-transformed signals obtained by performing Fouriertransform of the output m number of intermediate signals; said inversesplitter to supply the output m number of Fourier-transformed signals tosaid unitary matrix demodulator; said unitary matrix demodulator todemodulate a signal associated with a unitary matrix having m rows and mcolumns whose components other than whose diagonal components are 0,from a matrix having m rows and m columns in which each of the suppliedm number of Fourier-transformed signals is its diagonal component andcomponents other than the diagonal components are 0, and output thesignal as a demodulated signal; and said parallel-serial converter toparallel-serial-convert the demodulated plurality of demodulated signalsto output them as a signal having been transmitted, and wherein adifference between frequencies of any two of channels of said Fouriertransform unit is equal to or larger than a predetermined coherentbandwidth.
 7. A transmitter apparatus, comprising a serial-parallelconverter, a plurality of unitary matrix modulators, a splitter, aninverse Fourier transform unit, a parallel-serial converter, and atransmission unit, wherein: said serial-parallel converter receives aninput of a signal to be transmitted, and serial-parallel-converts thesignal to output m×n (m≧2, n×1) number of intermediate signals; saidplurality of unitary matrix modulators each modulate any m number ofsignals of the output m×n number of intermediate signals, with nodoubles, into a unitary matrix having m rows and m columns whosecomponents other than whose diagonal components are 0, and output theobtained matrix; said splitter supplies the respective diagonalcomponents of the output matrix to input channels of said inverseFourier transform unit as input channels; said inverse Fourier transformunit outputs m number of inverse-Fourier-transformed signals obtained byperforming inverse Fourier transform of the input signals supplied tothe input channels thereof; said parallel-serial converterparallel-serial-converts the output m number ofinverse-Fourier-transformed signals to output one transmission signal;and said transmission unit transmits the output transmission signal, andwherein among any two channels of said inverse Fourier transform unit,any two channels to which the diagonal components of the matrix outputfrom said plurality of unitary matrix modulators are supplied havetherebetween a frequency difference which is equal to or larger than apredetermined coherent bandwidth.
 8. The transmitter apparatus accordingto claim 7, wherein a diagonal component on a j-th row and a j-th columnof a matrix output 15 from an i-th one of the plurality of unitarymatrix modulators (where 0≦i<n, 0>j<m) is supplied to a j×m+i-th inputchannel of said inverse Fourier transform unit.
 9. A receiver apparatus,comprising a reception unit, a serial-parallel converter, a Fouriertransform unit, an inverse splitter, a plurality of unitary matrixdemodulators, and a parallel-serial converter, wherein: said receptionunit receives a transmission signal having been transmitted, and outputsthis as a reception signal; said serial-parallel converterserial-parallel-converts the output reception signal to output m×n (m≧2,n≧1) number of intermediate signals; said Fourier transform unit outputsm×n number of Fourier-transformed signals obtained by performingFourier-transform of the output m×n number of intermediate signals; saidinverse splitter supplies n number of signals of the output m×n numberof Fourier-transformed signals to each of said unitary matrixdemodulators with no doubles; each of said plurality of unitary matrixdemodulators demodulates a signal associated with a unitary matrixhaving m rows and m columns whose components other than whose diagonalcomponents are 0, from a matrix having m rows and m columns in whicheach of the supplied m number of Fourier-transformed signals is itsdiagonal component and components other than the diagonal components are0, and outputs this as a demodulated signal; and said parallel-serialconverter parallel-serial-converts the plurality of demodulated signalshaving been demodulated, and outputs them as signals having beentransmitted, and wherein among any two channels of said Fouriertransform unit, any two channels that are to output Fourier-transformedsignals to be supplied to each of said plurality of unitary matrixdemodulators have therebetween a frequency difference which is equal toor larger than a predetermined coherent bandwidth.
 10. The receiverapparatus according to claim 9, wherein each of said plurality ofunitary matrix demodulators compares each of a plurality ofpredetermined unitary matrices which each have m rows and m columns andwhose components other than whose diagonal components are 0, with amatrix having m rows and m columns in which each of the supplied mnumber of Fourier-transformed signals is its diagonal component andcomponents other than the diagonal components are 0, selects one of theplurality of predetermined unitary matrices that has a smallestEuclidean distance, and obtains the selected one as a demodulationresult.
 11. The receiver apparatus according to claim 10, wherein adiagonal component on a j-th row and a j-th column of the matrixcompared by an i-th one of said plurality of unitary matrix demodulators(where 0≦i<n, 0≦j<m) is one that has been output from a j×m+i-th outputchannel of said inverse Fourier transform unit.
 12. A program forcontrolling a computer to function as a serial-parallel converter, aplurality of unitary matrix modulators, a splitter, an inverse Fouriertransform unit, a parallel-serial converter, and a transmission unit,wherein in said computer, said program controls: said serial-parallelconverter to receive an input of a signal to be transmitted andserial-parallel-convert the signal to output m×n (m≧2, n≧1) number ofintermediate signals; said plurality of unitary matrix modulators toeach modulate any m number of signals of the output m×n number ofintermediate signals, with no doubles, into a unitary matrix having mrows and m columns whose component other than whose diagonal componentsare 0, and output the obtained matrix; said splitter to supply therespective diagonal components of the output matrix to input channels ofsaid inverse Fourier transform unit as input channels; said inverseFourier transform unit to output m number of inverse-Fourier-transformedsignals obtained by performing inverse Fourier transform of the inputsignals supplied to the input channels thereof; said parallel-serialconverter to parallel-serial-convert the output m number ofinverse-Fourier-transformed signals to output one transmission signal;and said transmission unit to transmit the output transmission signal,and wherein among any two channels of said inverse Fourier transformunit, any two channels to which the diagonal components of the matrixoutput from said plurality of unitary matrix modulators are suppliedhave therebetween a frequency difference which is equal to or largerthan a predetermined coherent bandwidth.
 13. The program according toclaim 12, which controls said computer to function in a manner that adiagonal component on a j-th row and a j-th column of a matrix outputfrom an i-th one of the plurality of unitary matrix modulators (where0≦i<n, 0≦j<m) is supplied to a j×m+i-th input channel of said inverseFourier transform unit.
 14. A program for controlling a computer tofunction as a reception unit, a serial-parallel converter, a Fouriertransform unit, an inverse splitter, a plurality of unitary matrixdemodulators, and a parallel-serial converter, wherein in said computer,said program controls: said reception unit to receive a transmissionsignal having been transmitted, and output this as a reception signal;said serial-parallel converter to serial-parallel-convert the outputreception signal to output m×n (m≧2, n≧1) number of intermediatesignals; said Fourier transform unit to output m×n number ofFourier-transformed signals obtained by performing Fourier-transform ofthe output m×n number of intermediate signals; said inverse splitter tosupply n number of signals of the output m×n number ofFourier-transformed signals to each of said unitary matrix demodulatorswith no doubles; each of said plurality of unitary matrix demodulatorsto demodulate a signal associated with a unitary matrix having m rowsand m columns whose components other than whose diagonal components are0, from a matrix having m rows and m columns in which each of thesupplied m number of Fourier-transformed signals is its diagonalcomponent and components other than the diagonal components are 0, andoutput this as a demodulated signal; and said parallel-serial converterto parallel-serial-convert the plurality of demodulated signals havingbeen demodulated, and outputs them as signals having been transmitted,and wherein among any two channels of said Fourier transform unit, anytwo channels that are to output Fourier-transformed signals to besupplied to each of said plurality of unitary matrix demodulators havetherebetween a frequency difference which is equal to or larger than apredetermined coherent bandwidth.
 15. The program according to claim 14,which controls said computer in a manner that each of said plurality ofunitary matrix demodulators compares each of a plurality ofpredetermined unitary matrices which each have m rows and m columns andwhose components other than whose diagonal components are 0, with amatrix having m rows and m columns in which each of the supplied mnumber of Fourier-transformed signals is its diagonal component andcomponents other than the diagonal components are 0, selects one of theplurality of predetermined unitary matrices that has a smallestEuclidean distance, and obtains the selected one as a demodulationresult.
 16. The program according to claim 15, which controls saidcomputer to function in a manner that a diagonal component on a j-th rowand a j-th column of the matrix compared by an i-th one of saidplurality of unitary matrix demodulators (where 0≦i<n, 0≦j<m) is onethat has been output from a j×m+i-th output channel of said inverseFourier transform unit.